It is known that .alpha.-adrenergic receptors are subdivided into .alpha..sub.1 and .alpha..sub.2 receptors essentially on the basis of their response to specific agonist and antagonist agents. The .alpha..sub.2 receptors are located at the noradrenergic nerve endings where such receptors are involved in the release of noradrenaline. The .alpha..sub.2 receptors are also present in various tissues as, for example, in the pancreas, in blood platelets, in adipose tissues, in blood vessels and in the brain.
Blocking agents for .alpha..sub.2 adrenergic are of therapeutic interest for the treatment of ailments of the central nervous system, such as depressive illness and cerebral aging, for treatment of some cardiac deficiencies and asthma and for the prophylactic and curative treatment of ailments in which platelet hyper-aggregability is involved such as migraine and thrombotic ailments. Further, .alpha..sub.2 blocking agents are of value as diuretic and anorexigenic agents and for the treatment of metabolic troubles such as diabetes and obesity, as well as of certain forms of hypertension and of sexual inadequacies.
Although non-selective .alpha.-adrenergic blocking agents such as yohimbine and rauwolscine have been known for several years, few classes of compounds are known which provide selective .alpha..sub.2 blocking activity. One of these classes, for example, comprises imidazoline derivatives of 2,3-dihydrobenzofuran such as disclosed in GB Pat. No. 2,102,422. Another class comprises imidazoline derivatives of 1,4-benzodioxan, such as disclosed in EP Pat. Appl. 092,328 and GB Pat. No. 2,068,376 of which 2-[2-(1,4-benzodioxanyl)]-2-imidazoline hydrochloride (Idazoxan hydrochloride) seems the compound of most interest. Another class of compounds comprises 2-[(1,4-benzodioxan-2-yl)alkyl]imidazoles such as described by J. M. Caroon, et al., J. Med. Chem., 25, 666-670 (1982). A further class of compounds comprises 4(5)-(phenylalkylimidazoles, 4(5)-(phenylalkanoyl)-imidazoles and 4(5) [(phenyl)hydroxyalkyl]imidazoles, such as described in EP Pat. Appl. 034,473. Also European patent application No. 86870010.5 describes certain compounds as having .alpha..sub.2 adrenergic receptor blocking activity, namely, 4(5)-(biphenylalkyl)imidazoles, 4(5)-(biphenylalkenyl)imidazoles and 4(5)-[(biphenyl)hydroxyalkyl]imidazoles. U.S. Pat. No. 4,281,141 discloses 4-[2,2,2,-(phenyl)(pyridyl)(cyano)ethyl]imidazole derivatives as having activity as fungicides.
Lilly U.S. Pat. No. 4,605,661 to Hirsch et al shows 4(5)-(2,2-diarylethyl)imidazoles as aromatase enzyme inhibitors useful for treatment of estrogen dependent disorders. In particular, the compound 4(5)-(2,2-diphenylethyl)imidazole is described. There is no mention, however, of any specific pyridylethylimidazole compound.